MacViews: Support -[NSWindow close] on sheets.

ui/views/cocoa/widget_owner_nswindow_adapter.mm

Index: ui/views/cocoa/widget_owner_nswindow_adapter.mm
diff --git a/ui/views/cocoa/widget_owner_nswindow_adapter.mm b/ui/views/cocoa/widget_owner_nswindow_adapter.mm
index b40ea57f523cfa5353fe51c5b4e5e388a8e34349..6e62398ca3972cd2fd75c9e3fbb272adc3bd68f5 100644
--- a/ui/views/cocoa/widget_owner_nswindow_adapter.mm
+++ b/ui/views/cocoa/widget_owner_nswindow_adapter.mm
@@ -84,7 +84,8 @@ void WidgetOwnerNSWindowAdapter::OnWindowWillClose() {
 
   // AppKit child window relationships break when the windows are not visible,
   // so if the child is not visible, it won't currently be a child.
-  DCHECK(![child_window isVisible] || [child_window parentWindow]);
+  if (![child_window isVisible])
+    DCHECK(![child_window parentWindow] && ![child_window sheetParent]);
   DCHECK([child_window delegate]);
 
   [child_window close];